The present invention relates to eye-examining methods in general, and more particularly to a method of determining the proper individually given positions of dioptric portions on eyeglasses, especially on pantoscopic eyeglasses for the close-range positions of the eyes of an examinee.
Pantoscopic eyeglasses usually have a relatively small close-range or reading-range regions, such regions having, for instance, a diameter of 6 millimeters.
In the close-range or reading-range position of the eyes, in which the eyes are moved somewhat downwardly and also somewhat inwardly because of the shorter observation distance, the close-range regions should be arranged within the observation direction as exactly as possible. When the close-range region or portion is positioned exactly on the respective eyeglass, the user of the eyeglasses can sharply discern the respective line of writing or print from the beginning of the line to the end thereof during normal sweep of the eyes, provided that the length of the line is within a certain limit which is determined by the size of the close-range dioptric portion and hence by the angle through which the respective eye can move while still looking through the respective close-range dioptic portion. To satisfy the above condition, it must be assured that, as the eyes are moved from side to side while reading the respective line, the points of intersection of the line of direct vision, which moves in accordance with the angular displacement of the respective eye, with the respective eyeglass are still located within the close-range dioptric portion of the respective eyeglass. On the other hand, when the angular displacement of the respective eye is more pronounced, the above-discussed points of intersection become located outside of the close-range dioptric portion so that the user of the eyeglasses sees the script or the like only as a blurred image.
Heretofore, it was resorted to the use of experimental values for determining the positions of the dioptric portions on the pantoscopic eyeglasses in the reading position of the eyes of the examinee. These experimentally obtained values were used to locate the center of the close-range dioptric portion with respect to the center of the far-range portion of the respective eyeglass as a whole. For instance, it was heretofore customary to measure 2.5 millimeters inwardly and 14 millimeters downwardly from the center of the far-range portion of the respective eyeglass to determine the location of the center of the close-range portion of the eyeglass.
This method which is based on experience and on experimentally obtained values is sufficiently accurate when used, for instance, for manufacturing bifocal eyeglasses. This is attributable to the fact that in these bifocal eyeglasses the close-range portion is substantially larger than in pantoscopic eyeglasses. The situation is different for pantoscopic eyeglasses where difficulties are often encountered in view of the fact that it is not possible to establish the proper positions of the close-range dioptric portions with a sufficient degree of accuracy. This is further aggravated by the fact that the proper positions of the close-range dioptric portions vary from one individual to another so that an exact and individual determination of the proper position of the close-range dioptric portions is impossible to achieve by resorting to the use of experimental values.